His last contact was through a third party from the outskirts of the town of Zawiya, which has seen fierce fighting in recent days.

The paper said in a statement: "The Guardian has been in contact with Libyan government officials in Tripoli and London and requested them to act urgently to discover where he is, if he is safe and well, and to establish if he is in the custody of the authorities."

The journalist, who has written for the Guardian since 2004, has spent long periods in Somalia, Sudan, Iraq and Afghanistan, reporting on the stories of ordinary people and their suffering.

He has won several prizes for his reporting, including foreign reporter of the year at the British Press Awards, the James Cameron award and the Martha Gellhorn prize.

News of his disappearance comes as a BBC team told how they were beaten, hooded and subjected to mock executions by Libyan troops and secret police.

The three men were detained on Monday as they tried, like many journalists, to get around government restrictions to reach Zawiya.